A variety of keyboard switch devices are commonly used for keyboard switches on typewriter keyboards or similar keyboards. The switches used may be membrane switches or other types, such as capacitance, or Hall effect switches.
The actuating assemblies used for such switches commonly comprise a frame, or housing, and a plunger which is slideably mounted in the frame such that when the plunger is depressed, the switch is closed. It is frequently a requirement that the switch provide a tactile effect for the operator; the term "tactile effect" is understood to mean that when the plunger is depressed, the operator experiences an abrupt decrease in the force required to depress the switch at an intermediate stage so that the operator is aware that the switch has been closed. Some keyboards provide the tactile effect while others do not; in the latter case, the force required to depress the plunger increases gradually and without an abrupt change. Many keyboards also require a shift lock type effect for one or more of the switch positions. When a shift lock key is depressed, the plunger is moved to its lowered position but its reverse movement is arrested by a mechanism on the actuator which holds the plunger in its depressed condition or a partially depressed condition. When the plunger is again depressed, the mechanism permits the plunger to return to its normal position.
Heretofore, it has been necessary for a keyboard switch manufacturer to use different actuator parts or to use different numbers of standard parts for the different modes of switch operation. In making an alpha numeric keyboard, for example, if the manufacturer would use one type of actuator for most of the key positions, such as the letters and numerals, the type of actuator used would be either a normal mode actuator (no tactile effect) or a tactile effect actuator. The manufacturer would, however, be required to use different plunger or frame parts for the shift lock keys of the keyboard. This requirement for different types of actuating mechanisms for the different operating modes has been burdensome in the past in that it required the manufacturer to design and obtain several different plunger or frame parts if he wished to produce a variety of types of keyboards.
The present invention is directed to the achievement of an improved keyboard switch actuator which comprises standard component parts which can be assembled to each other with the parts in one of several orientations and which will provide any one of the three desired operating modes (tactile effect, normal mode, shift lock) depending upon the orientations of the parts at the time of assembly. The invention is further directed to the achievement of a switch actuator comprising a reduced number of component parts which can be produced by molding processes.
A switch actuating assembly in accordance with the invention comprises a frame having a fixed end and a free end and a plunger mounted on the frame. The plunger has a lower end which is proximate to the fixed end of the frame and a force-receiving end which is proximate to the free end of the frame. The plunger is slideably mounted on the frame and is movable from a normal or extended position to a depressed position when force is applied to the force-receiving end of the plunger. The force-receiving end is located beyond the free end of the frame when the plunger is in the normal position and is moved towards the free end of the frame when the plunger is depressed. The lower end of the plunger is moved towards the fixed end of the frame when the plunger is moved to the depressed position. Spring means are provided which are resiliently stressed when the plunger is moved to the depressed position, the spring means being effective to return the plunger to the normal position when force is removed from the force-receiving end. The switch actuating assembly of the invention is particularly characterized in that the plunger has a deflectable camming arm connected thereto proximate to the force-receiving end, the cam arm extending towards the lower end of the plunger and having a cam following free end. A first cam is provided on the frame which is between the cam following free end of the plunger and the fixed end of the frame when the plunger is in the normal position so that the cam following free end of the camming arm engages the first cam when the plunger is moved to the depressed position with resulting deflection of the camming arm. The deflection of the camming arm results in an abrupt change in the force required to depress the plunger and a tactile effect is provided to the switch operator.
In accordance with a further embodiment, the frame has a second cam thereon which is spaced in an angular sense from the first cam, the plunger being capable of assembly to the frame while the plunger is in a first orientation or in a second orientation. The cam following free end of the camming arm engages the first cam when the plunger is assembled to the frame while in the first orientation and engages the second cam when the plunger is assembled to the frame while in the second orientation. The second cam is contoured to provide a shift lock mode of operation in that the second cam permits movement of the free end of the camming rod therepast to the depressed position from the normal position, and the second cam is also contoured to arrest movement of the cam when the plunger moves from the depressed condition to the normal position so that the plunger is held in an intermediate position which is close to the depressed position. The second cam is further contoured to permit passage of the cam following free end and return of the plunger to the normal position following movement of the plunger from the intermediate position to the depressed position.
In accordance with further embodiments, the frame has an axial opening extending therethrough from the free end towards the fixed end and the plunger has guide portions which are slideably received in the axial opening. The plunger is capable, in accordance with further embodiments, of assembly to the frame while the plunger is in a third orientation relative to the frame and the frame has a clearance opening for the cam following free end of the camming arm when the plunger is in the third orientation so that the plunger can be moved from the normal position to the depressed position without a tactile effect.
In accordance with further embodiments, at least three integral plunger arms extend radially from the guide portions of the plunger at the force receiving end, the camming arm being integral with, and extending from, one of the radially extending plunger arms and the camming arm being parallel to the guide portions of the plunger. The frame has radially extending slots extending from the axial opening at the free end of the frame, the plunger arms being dimensioned to enter the radially extending slots when the plunger is moved to the depressed position. The orientation of the plunger in this embodiment is determined by the association of the radially extending plunger arms and the radially extending slots.
In accordance with further embodiments, the frame and plunger are each one piece molded parts and the spring means comprises a larger diameter helical spring and a smaller diameter helical spring.
In accordance with further embodiments, the actuator comprises a frame member and a plunger member, and camming arm being on one of the members and the cams are on the other member.